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Refactors CLI tests of the `create` command as the first batch of tests refactored to take a PTY out of the loop.
One interesting difference I noticed between PTY and a direct pipe to standard in is that on the PTY we write `\r` to enter some input, but the kernel actually sends `\n` (or maybe `\r\n`) to the process, at least on Unix. (On windows we sent `\r\n` into the PTY). This is reflected in the implementation of the `Writer` , otherwise mostly inspired by the PTYTest equivalents.
Relates to https://github.com/coder/internal/issues/1400
Extracts the code that matches command output from the code that sets up a PTY, so it can be used independently.
Subsequent PRs will actually refactor the tests to use this directly over an inmemory pipe.<!--
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Spike Curtis